Light emitting element and manufacturing method thereof, and light emitting device using the light emitting element

ABSTRACT

A light-emitting element has a layer including an organic material between a first electrode and a second electrode, and further has a layer including a metal oxide between the second electrode and the layer including the organic material, where these electrodes and layers are laminated so that the second electrode is formed later than the first electrode. The light-emitting element is suppressed damage caused to a layer including an organic material during deposition by sputtering and a phenomenon such as short circuit between electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting element that has astructure interposing a plurality of layers between a pair ofelectrodes, in particular, relates to a structure of the layers.

2. Description of the Related Art

A light-emitting device utilizing a light emission from anelectroluminescent element (a light-emitting element) has beenattracting attention as a device, for example, for displaying or forlighting.

As the light-emitting element that is used for the light-emittingdevice, an element that has a structure interposing a plurality oflayers, each including a material such as a luminescent or carriertransporting material, between a pair of electrodes is well known.

In the case of this light-emitting element, one of the electrodesfunctions as an anode while the other electrode functions as a cathode,a hole injected from the anode side and an electron injected from thecathode side are recombined to form a molecule in a excited state, andlight is emitted when the molecule returns to the ground state. Theemitted light is extracted outside through one or both of the pair ofelectrodes.

As for a manufacturing process of the light-emitting element above, itis commonly known to form one of the electrodes, form the plurality oflayers thereon, and form the other electrode further thereon.

In the case of manufacturing the light-emitting element in this way, thelayers are sometimes so damaged in the process of forming the electrodeafter forming the plurality of layers that favorable characteristicscannot be obtained. This phenomenon is frequently observed particularlyin the case of using sputtering to form the electrode. This is believedto be because high-energy atoms damage the layers in the process ofusing sputtering to form the electrode.

Consequently, a light-emitting element comprising a structure that isless subjected to damage even in the case of using sputtering to formthe electrode and a manufacturing method thereof have been developed.

For example, Patent Document 1 or Patent Document 2 shows that damage toan organic layer, which is caused during deposition by sputtering, canbe suppressed by providing a layer including phthalocyanine. Inaddition, Patent Document 3 also reports that damage to an organiclayer, which is caused during deposition by sputtering, can besuppressed by providing a layer including AgLi.

However, the method shown in Patent Document 1 or Patent Document 2 mayhave problems that, for example, a process is increased for providingthe layer including phthalocyanine between an electron transportinglayer and an electron injecting electrode and the luminous efficiency ina red light emission is decreased due to phthalocyanine that absorbslight in a long wavelength range easily. In addition, the method shownin Patent Document 3 may have problems that, for example, as the filmthickness of AgLi becomes thicker, the transmissivity of light becomeslower to decrease the external extraction efficiency of emitted light.

[Patent Document 1] Japanese Patent Laid-Open No. 2002-75658

[Patent Document 2] Japanese Patent Laid-Open No. 2002-359086

[Patent Document 3] Japanese Patent Laid-Open No. 2003-249357

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light-emittingelement formed to suppress damage, which is caused to a layer includingan organic material during deposition by sputtering. In addition, it isan object of the present invention to provide a light-emitting elementformed to suppress damage, which is caused to a layer including anorganic material during deposition by sputtering, and also to suppress aphenomenon such as short circuit between electrodes.

A light-emitting element according to the present invention is providedwith a layer including a metal oxide between a pair of electrodes inorder to suppress damage to a layer including an organic material, whichis likely to be caused during deposition by sputtering.

A light-emitting element according to the present invention has a layerincluding an organic material between a first electrode and a secondelectrode, and further has a layer including a metal oxide between thesecond electrode and the layer including the organic material, wherethese electrodes and layers are laminated so that the second electrodeis formed later than the first electrode.

The layer including the organic material may be a single layer or amultilayer. Preferably, a material such as a highly carrier (electron orhole) transporting material and a highly carrier injecting material arecombined to form the layer including the organic material so that alight-emitting region is formed in a portion that is away from the firstelectrode and the second electrode. Further, the layer including theorganic material may include a metal element such as lithium ormagnesium or another metal element in a portion thereof.

In addition, specific examples of the metal oxide include molybdenumoxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), tungstenoxide (WOx), manganese oxide (MnOx), and the like and it is preferredthat these are formed by evaporation.

In the case of the light-emitting element according to the presentinvention, as described above, which has the structure in which thelayer including the metal oxide is provided between the second electrodeand the layer including the organic material, the second electrode canbe formed by sputtering.

Therefore, as the second electrode, it becomes easier to use a materialthat is easier to deposit by sputtering than evaporation, for example,indium tin oxide (ITO), indium tin oxide containing silicon (ITSO), orIZO (Indium Zinc Oxide) of indium oxide mixed with zinc oxide (ZnO) at 2to 20%, and then, the material for forming the second electrode has awide range of choice.

In addition, even in the case of a light-emitting element of a structurethat has a film formed by sputtering between the second electrode andthe layer including the metal oxide, damage to a layer including anorganic material due to deposition by sputtering can be suppressed inthe same way as described above. In this case, it is not alwaysnecessary to form the second electrode by sputtering. The advantage ofthe present invention can be obtained as long as a light-emittingelement has a structure in which a layer including an organic material,a layer including a metal oxide, and a layer formed by sputtering arelaminated in order.

According to the present invention, it is possible to obtain alight-emitting element where a defect due to deposition by sputtering issuppressed. In addition, it is possible to obtain a light-emittingelement where a defect due to deposition by sputtering is suppressed andshort circuit between electrodes is also suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing voltage-luminance characteristics of alight-emitting element according to the present invention and alight-emitting element according to a comparative example;

FIGS. 2A to 2C are diagrams illustrating a structure of layers of alight-emitting element according to the present invention;

FIG. 3 is a diagram illustrating a structure of layers of alight-emitting element according to the present invention;

FIG. 4 is a diagram showing voltage-current characteristics of alight-emitting element according to the present invention and alight-emitting element according to a comparative example;

FIG. 5 is a diagram showing luminance-current efficiency characteristicsof a light-emitting element according to the present invention;

FIG. 6 is a diagram showing voltage-luminance characteristics oflight-emitting elements according to the present invention;

FIG. 7 is a diagram showing voltage-current characteristics oflight-emitting elements according to the present invention;

FIG. 8 is a diagram showing luminance-current efficiency characteristicsof light-emitting elements according to the present invention;

FIGS. 9A to 9C are diagrams illustrating cross-section structures oflight-emitting devices according to the present invention;

FIGS. 10 A and 10 B are diagrams illustrating cross-section structuresof light-emitting devices according to the present invention;

FIG. 11 is a top view of a pixel portion of a light-emitting deviceaccording to the present invention;

FIG. 12 is a top view of a pixel portion of a light-emitting deviceaccording to the present invention;

FIGS. 13A and 13B are circuit diagrams of pixel portions oflight-emitting devices according to the present invention;

FIG. 14 is a diagram illustrating a cross-section structure of alight-emitting device according to the present invention;

FIG. 15 is a view showing a frame format of a light-emitting deviceaccording to the present invention; and

FIG. 16 is a diagram of an electronic device mounted with alight-emitting device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

A light-emitting element according to the present invention has a layerincluding an organic material between a pair of electrodes. The layerincluding the organic material has a single layer or a plurality oflayers. Preferably, a layer including a highly carrier injectingmaterial and a layer including a highly carrier transporting materialare combined to form the layer including the organic material so that alight-emitting region is formed away from the electrodes, that is, sothat carriers are recombined in a portion that is away from theelectrodes.

One mode of the light-emitting element according to the presentinvention will be described below with reference to FIGS. 2A to 2C.

In the present embodiment mode, a light-emitting element 210 is providedover a substrate 200 for supporting the light-emitting element 210, andhas a first electrode 201, first to fifth layers 202 to 206 laminated onthe first electrode 201 in order, and a second electrode 207 furtherprovided thereon so that the first electrode 201 functions as a cathodeand the second electrode 207 functions as an anode.

As the substrate 200, for example, glass or plastic can be used. Anothermaterial other than these may be used as long as the material functionsas a support in a manufacturing process of a light-emitting element.

It is preferable that the first electrode 201 is formed to include amaterial that has a small work function (a work function of 3.8 eV orless) such as a metal, an alloy, an electrically conductive compound, ora mixture of these, which specifically include elements belonging toGroup 1 or Group 2 of the periodic table of the elements, that is, analkali metal such as lithium (Li) or cesium (Cs) and an alkali earthmetal such as magnesium (Mg), calcium (Ca), or strontium (Sr), and analloy including the element, for example, an aluminum alloy (Al:Li) or asilver alloy (Mg:Ag). However, by providing a layer that has a functionof promoting electron injections in contact with the first electrode 201between the first electrode 201 and the second electrode 207, variousconductive materials such as Al, Ag, indium tin oxide (ITO), and ITOcontaining silicon (Si) can be used as the first electrode 201regardless of magnitude of work function. In this regard, however,another materials other than the materials mentioned in the presentembodiment mode may be used.

The first layer 202 is a layer including a highly electron injectingmaterial, for example, a compound of an alkali metal or alkali earthmetal such as lithium fluoride (LiF), cesium fluoride (CsF), or calciumfluoride (CaF₂). In addition, the first layer 202 may be a layerincluding a highly electron transporting material and either an alkalimetal or an alkali earth metal, for example, a layer including Alq₃ andmagnesium (Mg).

The second layer 203 is a layer including a highly electron transportingmaterial, for example, a metal complex that has a quinoline moiety or abenzoquinoline moiety such as tris(8-quinolinolato)aluminum(abbreviation: Alq₃), tris(5-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]-quinolinato) beryllium(abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq). In addition, a metal complex that has a ligand such as an oxazoleor a thiazole, for example, bis[2-(2-hydroxyphenyl)-benzoxazolato]zinc(abbreviation: Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc(abbreviation: Zn(BTZ)₂), can be used. Further, in addition to the metalcomplexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviation: PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), andbathocuproin (abbreviation: BCP) can also be used. In this regard,however, another materials other than the materials mentioned in thepresent embodiment mode may be used.

The third layer 204 is a layer including a highly luminescent material.For example, a highly luminescent material such as N,N′-dimethylquinacridone (abbreviation: DMQd) or 2H-chromen-2-one (abbreviation:coumarin) and a highly carrier transporting material such astris(8-quinolinolato)aluminum (abbreviation: Alq₃) or9,10-di(2-naphthyl) anthracene (abbreviation: DNA) are freely combinedto form the third layer 204. However, since Alq₃ and DNA are also highlyluminescent materials, these materials may be used singularly as thethird layer 204.

The fourth layer 205 is a layer including a highly hole transportingmaterial, for example, an aromatic amine compound (that is, a compoundthat has a benzene ring-nitrogen bond) such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (abbreviation: α-NPD),4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (abbreviation:TPD), 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (abbreviation:TDATA), or4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(abbreviation: MTDATA). In this regard, however, another materials otherthan the materials mentioned in the present embodiment mode may be used.

The fifth layer 206 is a layer including a metal oxide such asmolybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx),tungsten oxide (WOx), or manganese oxide (MnOx). By providing the layerincluding the metal oxide in this way, it is possible to suppress damageto the layers respectively including organic compounds (the first tofourth layers in the present embodiment mode), which is caused in thecase of using sputtering in the process of forming the second electrode207. In the present embodiment mode, it is preferable that the layerincluding the metal oxide is formed by evaporation. In addition, it ispreferable that the layer including the metal oxide has a film thicknessof 10 nm or more. In order to suppress damage due to sputtering, it iseffective to form the layer including the metal oxide to have the filmthickness as mentioned above. As the layer including the metal oxide,another materials other than the materials mentioned in the presentembodiment mode may be used.

For example, the fifth layer 206 may be a layer including a metal oxideand a highly hole transporting material. Materials such as α-NPD and TPDdescribed above are cited as the highly hole transporting material. Byincluding the highly transporting material in this manner, it becomeseasier for the fifth layer 206 to generate holes. Additionally, bychanging the thickness of the fifth layer 206 including the highly holetransporting material to adjust a distance between a layer including ahighly light emitting material (the third layer 204 in this embodiment)and the second electrode 207, it becomes easier to extract lightemission showing a preferable spectrum to the outside. This is because aincrease of driving voltage that may be generated by making thethickness of the fifth layer 206 thicker can be reduced by including thehighly hole transporting material.

Further, in the case of forming the layer including the metal oxide tohave a film thickness of 100 nm or more, it is possible to suppressshort circuit between the first electrode 201 and the second electrode207, which is caused due to a factor such as a projection formed at afilm surface of the first electrode 201 or the second electrode 207 ordue to a foreign object mixed between these electrodes. Since the metaloxide has a high light-transmitting property, emitted light can beextracted sufficiently even when the film thickness becomes thicker.

It is preferable that the second electrode 207 is formed to include amaterial that has a large work function (a work function of 4.0 eV ormore) such as a metal, an alloy, an electrically conductive compound, ora mixture of these. Specifically, materials such as gold (Au), platinum(Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron(Fe), cobalt (Co), copper (Cu), palladium (Pd), and a nitride of a metal(such as TiN) can be used in addition to indium tin oxide (ITO), indiumtin oxide containing silicon, and IZO (Indium Zinc Oxide) of indiumoxide mixed with zinc oxide (ZnO) at 2 to 20%. In this way, a conductivematerial that can be deposited by sputtering is used to form the secondelectrode 207. In this regard, however, another materials other than thematerials mentioned in the present embodiment mode may be used.

In the light-emitting element according to the present invention, whichhas the structure described above, a current flows due to a potentialdifference generated between the first electrode 201 and the secondelectrode 207, a hole and an electron are recombined in the third layer204 that is the layer including the highly luminescent material, andthen, light is emitted. In other words, the light-emitting element hasthe structure so that a light-emitting region is formed in the thirdlayer 204. However, it is not necessary that the third layer 204 whollyfunction as a light-emitting region, and for example, a light-emittingregion may be formed only at a side of the second layer 203 or at a sideof the fourth layer 205 in the third layer 204.

Emitted light is extracted outside through one or both of the firstelectrode 201 and the second electrode 207. Therefore, one or both ofthe first electrode 201 and the second electrode 207 are formed toinclude a light-transmitting material.

In the case where both the first electrode 201 and the second electrode207 are formed to include a light-transmitting material, as shown inFIG. 2A, emitted light is extracted from both the substrate side and theside opposite to the substrate through the first electrode 201 and thesecond electrode 207. In the case where only the second electrode 207 isformed to include a light-transmitting material and in the case wherethe first electrode 201 and the second electrode 207 are formed toinclude a light-transmitting material and a reflective film is providedat the first electrode 201 side, as shown in FIG. 2B, emitted light isextracted from the side opposite to the substrate through the secondelectrode 207. In the case where only the first electrode 201 is formedto include a light-transmitting material and in the case where the firstelectrode 201 and the second electrode 207 are formed to include alight-transmitting material and a reflective film is provided at thesecond electrode 207 side, as shown in FIG. 2C, emitted light isextracted from the substrate side through the first electrode 201.

The layered structure provided between the first electrode 201 and thesecond electrode 207 is not limited to the structure described above. Astructure other than the structure described above may be used as longas a region where a hole and an electron are recombined is provided in aportion that is away from the first electrode 201 and the secondelectrode 207 in the structure in order to suppress quenching caused bymaking a light-emitting region and a metal come close to each other andthe structure has a layer including a metal oxide. In other words, thelaminated structure is not particularly limited, and layers respectivelyincluding materials such as a highly electron transporting material, ahighly hole transporting material, a highly electron injecting material,a highly hole injecting material, and a bipolar material (a highlyelectron and hole transporting material) may be freely combined with thelayer including the metal oxide to make the laminated structure.Further, the recombination region of carriers may be controlled byproviding a layer including, for example, an extremely thin siliconoxide film.

The light-emitting element described above is manufactured by formingthe first electrode 201 over the substrate 200, laminating the first tofifth layers 202 to 206 thereon in order, and forming the secondelectrode 207 further thereon. Although a method of forming each layeris not particularly limited, it is preferable that any of evaporation,inkjet, and spin coating is used to form the layer.

FIG. 3 shows a specific example of a light-emitting element according tothe present invention, which has a different structure from thestructure described above. A first electrode 301 is provided on asubstrate 300, and first to fifth layers 302 to 306 are provided on thefirst electrode 301 by laminating in order. Further, a second electrode307 is provided on the fifth layer 306.

Here, the first layer 302 is formed to include a highly hole injectingmaterial, the second layer 303 is formed to include a highly holetransporting material, the third layer 304 is formed to include a highlycarrier transporting material including a light emitter, and the fourthlayer 305 is formed to include a highly electron transporting material.The fifth layer 306 is a layer including a metal oxide, and in addition,may include a highly electron injecting material such as an alkali metalor an alkali earth metal such as lithium or magnesium. Also in the caseof the light-emitting element that has this structure, it is possible tosuppress damage to a layer including an organic compound due todeposition by sputtering, as described above. When the light-emittingelement has this structure, the first electrode 301 and the secondelectrode 307 function as an anode and a cathode, respectively. Thelight-emitting element shown in FIG. 3 is also one mode of thelight-emitting element according to the present invention, and thestructure of the light-emitting element according to the presentinvention is not limited to this.

In the thus described light-emitting element according to the presentinvention, damage to a layer including an organic material due tosputtering can be suppressed. In addition, short circuit between theelectrodes can be suppressed by controlling the film thickness of thelayer including the metal oxide. Furthermore, in a light-emitting deviceto which the light-emitting element according to the present inventionis applied, a defect of the light-emitting element due to sputtering orshort circuit between the electrodes is suppressed, and for example, ina display device, favorable display images can be obtained.

In the present embodiment mode, a case of forming an electrode bysputtering is described. However, for example, even in the case of alight-emitting element of a structure that has a film formed bysputtering between an electrode and a layer including a metal oxide, itis possible to obtain the advantage that damage to a layer including anorganic material due to sputtering can be suppressed in the same way asin the present embodiment mode. In either case, as long as alight-emitting element has a structure in which a layer including anorganic material, a layer including a metal oxide, and a layer formed bysputtering are laminated in order and the layer including the organicmaterial is formed before the layer formed by sputtering is formed, theadvantage of providing the layer including the metal oxide can beobtained.

Embodiment 1

A manufacturing method of a light-emitting element according to thepresent invention and characteristics of the light-emitting element willbe described. The structure or manufacturing process of thelight-emitting element according to the present invention is not limitedto the present embodiment, and a film thickness or a material, forexample, may be changed appropriately.

On a glass substrate, indium tin oxide (ITO) is deposited by sputteringto form a first electrode, where ITO in the deposition contains anamorphous component as its main component. Next, after etching ITO to beseparated into elements, a heat treatment is performed at 200° C. for 1hour. Further, after applying an acrylic that is a positive typephotoresist, exposure and development are performed to form a partitionlayer. After that, a heat treatment is performed at 220° C. for 1 hour.

Next, after wet cleaning, the glass substrate with ITO deposited isprocessed at 150° C. for 30 minutes in an atmosphere of vacuum of 1×10⁻⁶Pa after UV-ozone treatment.

Next, 4,4′-bis (5-methylbenzoxazol-2-yl) stilbene (abbreviation: BzOs)and lithium (Li) are co-deposited to form a first layer on the firstelectrode. The weight ratio of BzOs to Li is controlled to be 1:0.02. Inaddition, the film thickness of the first layer is controlled to be 20nm.

Next, Alq₃ is deposited to form a second layer on the first layer. Thefilm thickness of the second layer is controlled to be 20 nm.

Next, Alq₃ and DMQD are co-deposited to form a third layer on the secondlayer. The weight ratio of Alq₃ to DMQD is controlled to be 1:0.01. Inaddition, the film thickness of the third layer is controlled to be 40nm.

Next, α-NPD is deposited to form a fourth layer on the third layer. Thefilm thickness of the fourth layer is controlled to be 40 nm.

In this way, the layers respectively including the organic materials(the first to fourth layers) are formed on the first electrode. Thematerials included in the respective layers are not limited to thematerials mentioned in the present embodiment, and another materials maybe used.

Next, molybdenum oxide that is a metal oxide is deposited to form afifth layer on the fourth layer. The film thickness of the fifth layeris controlled to be 50 nm.

Next, ITO is deposited by sputtering to form a second electrode on thefifth layer. The substrate temperature during deposition (during plasmageneration) is 40° C. to 50° C. The deposited ITO contains an amorphouscomponent as its main component. The film thickness of the secondelectrode is controlled to be 110 nm.

Characteristics of the thus manufactured light-emitting elementaccording to the present invention are shown by circle points in FIG. 1.FIG. 1 shows voltage-luminance characteristics, where a horizontal axisindicates a voltage (V) and a vertical axis indicates a luminance(cd/m²). FIG. 1 indicates that a driving voltage (a voltage at which alight emission of 1 cd/m² or more is started is regarded as the drivingvoltage) is approximately 5.5 V. FIG. 4 shows voltage-currentcharacteristics, where a horizontal axis indicates a voltage (V) and avertical axis indicates a current (mA). FIG. 5 shows luminance(cd/m²)—current efficiency (cd/A) characteristics, where a horizontalaxis indicates a luminance and a vertical axis indicates a currentefficiency.

Comparative Example 1

A comparative example with respect to the light-emitting elementaccording to the present invention, shown in Embodiment 1, will bedescribed.

A light-emitting element of the present comparative example has astructure in which a mixed layer including BzOs and Li (20 nm), a layerincluding Alq₃ (20 nm), a mixed layer including DMQD and Alq₃ (40 nm), alayer including α-NPD (40 nm), and a layer including CuPc (20 nm) arelaminated in order on a first electrode including ITO, and a secondelectrode including ITO is further laminated thereon. In each case, ITOfor the electrode is formed by sputtering in the same way as describedabove. In addition, the weight ratio of BzOs to Li is 1:0.02, and theweight ratio of Alq₃ to DMQD is 1:0.01.

Characteristics of the light-emitting element of the present comparativeexample are shown by trigonal points in FIG. 1. FIG. 1 showsvoltage-luminance characteristics, where a horizontal axis indicates avoltage (V) and a vertical axis indicates a luminance (cd/m²). FIG. 1indicates that a driving voltage (a voltage at which a light emission of1 cd/m² or more is started is regarded as the driving voltage) isapproximately 13 V. FIG. 4 shows voltage-current characteristics, wherea horizontal axis indicates a voltage (V) and a vertical axis indicatesa current (mA). FIG. 5 shows luminance (cd/m²)-current efficiency (cd/A)characteristics, where a horizontal axis indicates a luminance and avertical axis indicates a current efficiency. The characteristics of thelight-emitting element are obtained from light emissions extracted fromthe second electrode side.

The characteristics of the light-emitting elements of Embodiment 1 andComparative Example 1, as shown above, indicate the following. In thecase of the light-emitting element of the comparative example usingCuPc, the driving voltage of the light-emitting element is high (13 V)due to damage to a portion of the element (a layer including an organicmaterial) in the process of depositing ITO by sputtering while thelight-emitting element according to the present invention has no such atendency. In other words, in the case of the light-emitting elementaccording to the present invention, the defect of the light-emittingelement due to sputtering can be more suppressed than in the case of thelight-emitting element of the comparative example.

Embodiment 2

In the present embodiment, a light-emitting element that has the samestructure as that shown in Embodiment 1 except that the fifth layerincluding molybdenum oxide has a different film thickness form that inEmbodiment 1 will be described. A manufacturing method of thelight-emitting element shown in the present embodiment is also the sameas that in Embodiment 1. Therefore, descriptions of the manufacturingmethod are omitted.

As for the light-emitting element of the present embodiment, the fifthlayer including molybdenum oxide has film thicknesses of 10 nm(Embodiment 2-1), 100 nm (Embodiment 2-2), and 200 nm (Embodiment 2-3).

Characteristics of the light-emitting elements of the present embodimentare shown in FIG. 6. FIG. 6 shows voltage-luminance characteristics,where a horizontal axis indicates a voltage (V) and a vertical axisindicates a luminance (cd/m²). FIG. 6 indicates that a driving voltage(a voltage at which a light emission of 1 cd/m² or more is started isregarded as the driving voltage) is approximately 5 V in each case oflight-emitting elements represented by Embodiments 2-1,2-2, and 2-3.FIG. 7 shows voltage-current characteristics, where a horizontal axisindicates a voltage (V) and a vertical axis indicates a current (mA).FIG. 8 shows luminance (cd/m²)-current efficiency (cd/A)characteristics, where a horizontal axis indicates a luminance and avertical axis indicates a current efficiency. FIGS. 6 to 8 indicate thatthe characteristics of the light-emitting elements are comparable toeach other regardless of the film thickness of the fifth layer when alower voltage is applied, and that the light-emitting element that hasthe fifth layer with the thicker film thickness has a tendency to show ahigher luminance when a higher voltage is applied. From here onwards, itis believed that damage due to sputtering can be more suppressed in thecase of the light-emitting element that has the fifth layer with thethicker film thickness. The characteristics of the light-emittingelements are obtained from light emissions extracted from the secondelectrode sides.

As described above, as for the light-emitting element shown in thepresent embodiment, it is determined that favorable characteristics canbe obtained even when the film thickness of the layer including themetal oxide is made thicker. Therefore, short circuit between theelectrodes can be suppressed by thickening the film thickness of thelayer including the metal oxide. Further, as for the light-emittingelement shown in the present embodiment, it is determined that emittedlight can be extracted outside efficiently even when the film thicknessof the layer including the metal oxide is thicker.

Embodiment 3

In the present embodiment, a structure of a light-emitting deviceaccording to the present invention will be described.

In each of FIGS. 9A to 9C, a portion surrounded by a dotted line is atransistor 11 provided for driving a light-emitting element 12. Thelight-emitting element 12 is formed to include a first electrode 13, asecond electrode 14, and a light-emitting layer 15 interposed betweenthese electrodes. The first electrode 13 and a drain of the transistor11 are electrically connected to each other by a wiring 17 runningthrough a first interlayer insulating film 16 a to 16 c. In addition,the light-emitting element 12 is separated by a partition layer 18 fromanother light-emitting element provided adjacently. A light-emittingdevice that has this structure according to the present invention isprovided over substrate 10.

In the light-emitting device that has the structure described above, thelight-emitting element 12 is a light-emitting element according to thepresent invention, and particularly, the light-emitting layer 15includes the above-mentioned layer including the metal oxide as acomponent.

The transistor 11 is included in a top-gate type. However, the structureof the transistor 11 is not particularly limited. For example, aninversely staggered TFT as shown in FIG. 10A may be used. In the case ofan inversely staggered TFT, a TFT where a protective film is formed on asemiconductor layer that forms a channel (a channel-protection TFT) maybe used as shown in FIG. 10B, or a TFT where a portion of asemiconductor layer that forms a channel is concave (a channel-etch) maybe used. Here, reference numerals 21, 22, 23, 24, 25, and 26 denote agate electrode, a gate insulating film, a semiconductor layer, an n-typesemiconductor layer, an electrode, and a protective film, respectively.

In addition, a semiconductor layer forming the transistor 11 may beeither crystalline or amorphous, or alternatively, may besemi-amorphous.

The following will describe a semi-amorphous semiconductor. Thesemi-amorphous semiconductor is a semiconductor that has an intermediatestructure between amorphous and crystalline (such as single-crystal orpolycrystalline) structures and has a third state that is stable interms of free energy, which includes a crystalline region that has shortrange order and lattice strain. Further, a crystal grain from 0.5 to 20nm is included in at least a region in a film of the semi-amorphoussemiconductor. A raman spectrum of the semi-amorphous semiconductor hasa shift to a lower wavenumber side than 520 cm⁻¹. In X-ray diffraction,diffraction peaks of (111) and (220) due to a Si crystal lattice areobserved. Hydrogen or halogen is included at 1 atom % or more in thesemi-amorphous semiconductor to terminate a dangling bond. Therefore,the semi-amorphous semiconductor is also referred to as amicro-crystalline semiconductor. A nitride gas is decomposed by glowdischarge (plasma CVD) to form the semi-amorphous semiconductor. As thenitride gas, in addition to SiH₄, a gas such as Si₂H₆, SiH₂Cl₂, SiHCl₃,SiCl₄, or SiF₄ can be used. This nitride gas may be diluted with H₂ orwith H₂ and one kind or plural kinds of rare gas elements selected fromHe, Ar, Kr, and Ne, where the dilution ratio is in the range of 2:1 to1000:1. The pressure during glow discharge is approximately in the rangeof 0.1 Pa to 133 Pa, and the power supply frequency is in the range of 1MHz to 120 MHz, preferably 13 MHz to 60 MHz. The substrate heatingtemperature may be 300° C. or less, preferably 100 to 250° C. It isdesirable to control an impurity of an atmospheric constituent such asoxygen, nitrogen, or carbon to have a concentration of 1×10²⁰/cm³ orless as an impurity element in the film, in particular, the oxygenconcentration is controlled to be 5×10¹⁹/cm³ or less, preferably1×10¹⁹/cm³ or less. In addition, a TFT (thin film transistor) using thesemi-amorphous semiconductor has a mobility of approximately 1 to 10m²/Vsec.

Further, specific examples of crystalline semiconductors for thesemiconductor layer include single-crystal or polycrystalline siliconand silicon-germanium, which may be formed by laser crystallization ormay be formed by crystallization with solid-phase growth using anelement such as nickel.

In the case of using an amorphous material, for example, amorphoussilicon to form the semiconductor layer, it is preferable that thelight-emitting device has a circuit in which the transistor 11 and theother transistor (a transistor forming the circuit for driving thelight-emitting element) are all n-channel transistors. Other than thatcase, the light-emitting device may have a circuit including one of ann-channel transistor and a p-channel transistor or may have a circuitincluding both an n-channel transistor and a p-channel transistor.

Further, the first interlayer insulating film 16 a to 16 c may be amultilayer as shown in FIGS. 9A and 9C, or may be a single layer. Thefirst interlayer insulating film 16 a includes an inorganic materialsuch as silicon oxide or silicon nitride, and the first interlayerinsulating film 16 b includes a material with self-flatness such asacrylic, siloxane (a material that has a framework structure formed of abond between silicon (Si) and oxygen (O) and includes at least hydrogenas a substituent), silicon oxide that can be used in coating fordeposition. In addition, the first interlayer insulating film 16 c has asilicon nitride film including argon (Ar). The materials included in therespective layers are not particularly limited, and therefore materialsother than the materials mentioned here may be used. Further, a layerincluding a material other than these materials may be combined. In thisway, both of an inorganic material and an organic material, or one of aninorganic material and an organic material may be used to form the firstinterlayer insulating film 16.

As for the partition layer 18, it is preferable that an edge portion hasa shape varying continuously in curvature radius. In addition, amaterial such as acrylic, siloxane, resist, or silicon oxide is used toform the partition layer 18. One or both of an inorganic material and anorganic material may be used to form the partition layer 18.

In each of FIGS. 9A and 9C, only the first interlayer insulating film 16is provided between the transistor 11 and the light-emitting element 12.However, as shown in FIG. 9B, a second interlayer insulating film 19 (19a and 19 b) may be provided in addition to the first interlayerinsulating film 16 (16 a and 16 b). In the light-emitting device shownin FIG. 9B, the first electrode 13 is connected to the wiring 17 throughthe second interlayer insulating film 19.

The second interlayer insulating film 19 may be a multilayer or a singlelayer in the same way as the first interlayer insulating film 16. Thesecond interlayer insulating film 19 a includes a material withself-flatness such as acrylic, siloxane (a material that has a frameworkstructure formed of a bond between silicon (Si) and oxygen (O) andincludes at least hydrogen as a substituent), silicon oxide that can beused in coating for deposition. In addition, the second interlayerinsulating film 19 b has a silicon nitride film including argon (Ar).The materials included in the respective layers are not particularlylimited, and therefore materials other than the materials mentioned heremay be used. Further, a layer including a material other than thesematerials may be combined. In this way, both of an inorganic materialand an organic material, or one of an inorganic material and an organicmaterial may be used to form the second interlayer insulating film 19.

In the light-emitting element 12, in the case where both the firstelectrode 13 and the second electrode 14 are formed to include alight-transmitting material, emitted light can be extracted from boththe first electrode 13 side and the second electrode 14 side asindicated by outline arrows of FIG. 9A. In the case where only thesecond electrode 14 is formed to include a light-transmitting material,emitted light can be extracted from only the second electrode 14 side asindicated by an outline arrow of FIG. 9B. In this case, it is preferablethat the first electrode 13 includes a highly reflective material orthat a film including a highly reflective material (a reflective film)is provided below the first electrode 13. In the case where only thefirst electrode 13 is formed to include a light-transmitting material,emitted light can be extracted from only the first electrode 13 side asindicated by an outline arrow of FIG. 9C. In this case, it is preferablethat the second electrode 14 includes a highly reflective material orthat a reflective film is provided above the second electrode 14.

In addition, in the case of the light-emitting element 12, the firstelectrode 13 may function as an anode while the second electrode 14functions as a cathode, or alternatively, the first electrode 13 mayfunction as a cathode while the second electrode 14 functions as ananode. However, the transistor 11 is a p-channel transistor in theformer case, and the transistor 11 is an n-channel transistor in thelatter case.

The light-emitting device of the present embodiment has a plurality oflight-emitting elements (however, not shown in the figures). In the casewhere the emission wavelength of each light-emitting element is the sameas the emission wavelength of the light-emitting element 12, thelight-emitting device emits monochromatic light. In the case where theemission wavelength of each light-emitting element is different, thelight-emitting device is able to emit light of a plurality of colorssuch as red (R), green (G), and a blue (B).

In the case of the above-mentioned light-emitting device, alight-emitting or non light-emitting state is controlled by a transistorelectrically connected to each light-emitting element. By controlling alight-emitting or non light-emitting state of each light-emittingelement, image display and the like are possible. In the light-emittingdevice, by applying the present invention, a defect due to a factor suchas sputtering or short circuit between electrodes, which is likely to becaused in a manufacturing process of the light-emitting element, issuppressed, and favorable images can be displayed.

Embodiment 4

In the present embodiment, light-emitting devices according to thepresent invention will be described with reference to top views of FIGS.11 and 12 and circuit diagrams of FIGS. 13A and 13B.

FIG. 11 shows a top view of a pixel portion of a light-emitting devicethat has a function of displaying. In the pixel portion, alight-emitting element, a driving transistor 7001 that determines alight-emitting or non light-emitting state of the light-emitting elementin accordance with an image signal, a switching transistor 7002 thatcontrols an input of the image signal, an erasing transistor 7003 thatcontrols the light-emitting element to be a non light-emitting stateregardless of the image signal, a source signal line 7004, a first scanline 7005, a second scan line 7006, and a current supply line 7007 areprovided. The light-emitting element according to the present inventionis formed in a region 7008. In addition, FIG. 13A shows a driver circuitdiagram of a pixel portion of a light-emitting device that has the pixelstructure shown in FIG. 11.

When the first scan line 7005 is selected in a writing period, theswitching transistor 7002 that has a gate connected to the first scanline 7005 is turned on. Then, when a video signal input to the sourcesignal line 7004 is input to a gate of the driving transistor 7001through the switching transistor 7002, a current flows from the currentsupply line 7007 to the light-emitting element to emit light. In aretention period, the switching transistor 7002 is turned off bycontrolling the electric potential of the first scan line 7005 to retainthe electric potential of the video signal written in the writingperiod. In an erasing period, since the second scan line 7006 isselected to turn on the erasing transistor 7003 to turn off the drivingtransistor 7001, a state in which no current is supplied to thelight-emitting element can be produced compellingly.

FIG. 12 shows a top view of a pixel portion of a light-emitting devicethat has a function of displaying, which has a different circuitstructure from FIG. 11. In the pixel portion, a driving transistor 7101that has a fixed gate potential, a switching transistor 7102 thatcontrols an input of the image signal, an erasing transistor 7103 thatcontrols the light-emitting element to be a non light-emitting stateregardless of the image signal, a current controlling transistor 7104that controls a current supply to the light-emitting element, a sourcesignal line 7105, a first scan line 7106, a second scan line 7107, acurrent supply line 7108, and a power line 7109 are provided. Thelight-emitting element according to the present invention is formed in aregion 7110. In addition, FIG. 13B shows a driver circuit diagram of apixel portion of a light-emitting device that has the pixel structureshown in FIG. 12.

When the first scan line 7106 is selected in a writing period, theswitching transistor 7102 that has a gate connected to the first scanline 7106 is turned on. Then, when a video signal input to the sourcesignal line 7105 is input to a gate of the current controllingtransistor 7104 through the switching transistor 7102, a current flowsfrom the current supply line 7108 to the light-emitting element throughthe driving transistor 7101 to emit light. The driving transistor 7101has a gate electrode connected to the power line 7109. In a retentionperiod, the switching transistor 7102 is turned off by controlling theelectric potential of the first scan line 7106 to retain the electricpotential of the video signal written in the writing period. In anerasing period, since the second scan line 7107 is selected to turn onthe erasing transistor 7103 to turned off the current controllingtransistor 7104, a state in which no current is supplied to thelight-emitting element can be produced compellingly.

In the above-mentioned light-emitting devices, the structure of eachtransistor is not particularly limited. A single-gate structure or amulti-gate structure may be used. In addition, an LDD structure may beused, or a gate-overlap LDD structure in which an LDD portion isoverlapped with a gate electrode may be used.

In the light-emitting devices shown in the present embodiment, byapplying the present invention, a defect due to a factor such assputtering or short circuit between electrodes is suppressed so thatfavorable images can be displayed.

Embodiment 5

The light-emitting devices according to the present invention, which areshown in Embodiments 3 and 4, are mounted in various electronic devicesafter attaching an external input terminal and sealing.

In these electronic devices according to the present invention, a defectin displaying due to a defect of a light-emitting element (damage to alight-emitting element) is suppressed, and favorable images can bedisplayed.

In the present embodiment, a light-emitting device according to thepresent invention and an electronic device mounted with thelight-emitting device will be described with reference to FIGS. 14, 15,and 16. However, the light-emitting device and electronic device shownin FIGS. 14, 15, and 16 are just one example, and the structure of thelight-emitting device is not to be considered limited to the presentembodiment.

FIG. 14 is a cross-section view of a light-emitting device aftersealing. A substrate 6500 and a sealing substrate 6501 are bonded with asealing agent 6502 to sandwich a transistor and a light-emitting elementaccording to the present invention in between. An FPC (Flexible PrintedCircuit) 6503 that serves as an external input terminal is attached toan edge of the substrate 6500. In addition, a region sandwiched betweenthe substrate 6500 and the sealing substrate 6501 is filled with aninert gas such as nitrogen or a resin material.

FIG. 15 is an overhead view of showing a frame format of thelight-emitting device according to the present invention. In FIG. 15,portions 6510, 6511, and 6512 shown by dashed lines are a driver circuitportion (a source side driver circuit), a pixel portion, and a drivercircuit portion (a gate side driver circuit). In the pixel portion 6511,the light-emitting element according to the present invention isprovided. The driver circuit portions 6510 and 6512 are connectedthrough the FPC 6503 that serves as an external input terminal and agroup of wiring formed on the substrate 6500. By receiving signals suchas a video signal, a clock signal, a start signal, and a reset signalfrom the FPC (Flexible Printed Circuit) 6503, the signals are input tothe source side driver circuit 6510 or the gate side driver circuit6512. Further, a printed wiring board (PWB) 6513 is attached to the FPC6503. In the driver circuit portion 6510, a shift resister 6515, aswitch 6516, and memories (latches) 6517 and 6518 are provided. In thedriver circuit portion 6512, a shift resister 6519 and a buffer 6520 areprovided. In addition to these, another function may be provided.

FIG. 16 shows an example of an electronic device mounted with thelight-emitting device according to the present invention.

FIG. 16 shows a laptop personal computer manufactured according to thepresent invention, which includes a main body 5521, a frame body 5522, adisplay portion 5523, and a keyboard 5524. A display device can becompleted by incorporating a light-emitting device that has alight-emitting element according to the present invention into apersonal computer.

In the present embodiment, the laptop personal computer is described.However, in addition, a light-emitting device that has a light-emittingelement according to the present invention may be mounted in a devicesuch as a cellular phone, a television, a car navigation system, or alighting apparatus.

This application is based on Japanese Patent Application serial no.2003-345579 filed in Japan Patent Office on 3th, Oct. 2003, the contentsof which are hereby incorporated by reference.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the present invention hereinafterdefined, they should be construed as being included therein.

1. (canceled)
 2. A light-emitting element comprising: an anode; acathode; a first layer comprising an organic material between the anodeand the cathode; and a second layer comprising a metal oxide and anelectron injecting material between the cathode and the first layer,wherein the second layer is in contact with the cathode, and wherein thefirst layer is in contact with the second layer.
 3. The light-emittingelement according to claim 2, wherein the electron injecting material isan alkali metal or an alkali earth metal.
 4. The light-emitting elementaccording to claim 2, wherein the cathode is formed over the secondlayer by sputtering.
 5. The light-emitting element according to claim 2,further comprising a substrate, wherein the anode is provided over thesubstrate, and wherein the cathode is provided over the anode.
 6. Thelight-emitting element according to claim 2, wherein the second layerhas a thickness of 100 nm or more.
 7. The light-emitting elementaccording to claim 2, wherein the metal oxide is one of molybdenumoxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganeseoxide.
 8. The light-emitting element according to claim 2, wherein thelight-emitting element is incorporated into at least one selected fromthe group consisting of a laptop personal computer, a cellular phone, atelevision, a car navigation system, and a lighting apparatus.
 9. Alight-emitting device comprising the light-emitting element according toclaim
 2. 10. A light-emitting element comprising: an anode; a cathode;and a layer comprising a metal oxide and an electron injecting materialbetween the anode and the cathode; wherein the layer is in contact withthe cathode.
 11. The light-emitting element according to claim 10,wherein the electron injecting material is an alkali metal or an alkaliearth metal.
 12. The light-emitting element according to claim 10,wherein the cathode is formed over the layer by sputtering.
 13. Thelight-emitting element according to claim 10, further comprising asubstrate, wherein the anode is provided over the substrate, and whereinthe cathode is provided over the anode.
 14. The light-emitting elementaccording to claim 10, wherein the metal oxide is one of molybdenumoxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganeseoxide.
 15. The light-emitting element according to claim 10, wherein thelayer has a thickness of 100 nm or more.
 16. The light-emitting elementaccording to claim 10, wherein the light-emitting element isincorporated into at least one selected from the group consisting of alaptop personal computer, a cellular phone, a television, a carnavigation system, and a lighting apparatus.
 17. A light-emitting devicecomprising the light-emitting element according to claim
 10. 18. Alight-emitting element comprising: an anode; a cathode; a first layercomprising a metal oxide and an electron injecting material between theanode and the cathode; and a second layer over the first layer, whereinthe second layer is formed by sputtering, and wherein the first layer isin contact with the second layer.
 19. The light-emitting elementaccording to claim 18, wherein the electron injecting material is analkali metal or an alkali earth metal.
 20. The light-emitting elementaccording to claim 18, further comprising a substrate, wherein the anodeis provided over the substrate, and wherein the cathode is provided overthe anode.
 21. The light-emitting element according to claim 18, whereinthe metal oxide is one of molybdenum oxide, vanadium oxide, rutheniumoxide, tungsten oxide, and manganese oxide.
 22. The light-emittingelement according to claim 18, wherein the first layer has a thicknessof 100 nm or more.
 23. The light-emitting element according to claim 18,wherein the light-emitting element is incorporated into at least oneselected from the group consisting of a laptop personal computer, acellular phone, a television, a car navigation system, and a lightingapparatus.
 24. A light-emitting device comprising the light-emittingelement according to claim 18.